1. Field of the Invention
The present invention generally relates to furniture having a spring mechanism for resiliently supporting a person during use, but being collapsible for compact storage, and, more particularly, to improvements in the structure, function, operation and assembly of such spring mechanisms.
2. Description of the Related Art
It is generally known that foldaway or foldable beds are attractive bedding options for persons with restricted living space, such as are commonly found in recreational vehicles, trailers, boats, studio apartments, and the like. A Murphy-style bed includes a mattress that can be swung or folded into a wall-mounted cabinet or closet when not being used for sleeping. A convertible foldable bed folds upon itself, either one or two times, for compact storage and to serve as a sofa or seating area, and then is unfolded into a bed for sleeping. The convertible sofa-bed includes a mattress that is sufficiently flexible to fold upon itself, and that is supported and deployed by an articulated bed frame.
Although generally satisfactory for their intended purposes, the known foldable beds have exhibited some drawbacks. For maximum sleeping comfort. the mattress is desired to be relatively firm and thick. However, a thick, firm mattress is not readily foldable, and certainly not in furniture of contemporary style where a low seat height and small dimensions are aesthetically desirable. In foldaway beds, a thick mattress requires a deeper cabinet or closet, thereby encroaching on the already limited living space. Where style and space requirements are paramount, a thin, foldable, soft and easily crushable mattress is employed; however, the result is often an unsatisfactory sleeping surface.
To solve the aforementioned problems, I have developed several spring mechanisms within mattresses, the mechanisms being collapsible for compact storage and being expandable for resiliently supporting a person during use. Reference can be made, for example, to my earlier patents, namely, U.S. Pat. No. 4,489,450; U.S. Pat. No. 4,654,905; U.S. Pat. No. 4,620,336; U.S. Pat. No. 5,184,809; U.S. Pat. No. 5,431,376; U.S. Pat. No. 5,535,460; U.S. Pat. No. 5,539,940; U.S. Pat. No. 5,539,944; U.S. Pat. No. 5,540,418; U.S. Pat. No. 5,524,305; U.S. Pat. No. 5,642,536 and U.S. Pat. No. 5,655,240.
As exemplified by these patents, each mechanism has an upper wire grid located below an upper mattress face, a lower wire grid located above a lower mattress face, and a system of generally planar, collapsible springs pivotably connected at opposite ends to the grids. When the mattress is in the body-supporting use position, the collapsible springs are upright in parallel planes generally parallel to head and foot end faces of the mattress. However, as the mattress is moved to the storage position, the collapsible springs pivot about the grids; and the upper and lower grids shift longitudinally and are drawn closer together, thereby decreasing the distance between the upper and lower mattress surfaces and decreasing the thickness of the mattress so that it can be compactly stored.
Experience has shown, however, that the collapsible spring mechanisms of these patents have certain shortcomings. One is the expense of production which is relatively high, primarily due to the requirement for special wire forming machinery. Another is the tendency of the collapsible springs to rotate beyond their upright position. Still another is the extent to which each collapsible spring can be compressed. Limited compression of collapsible springs render the mattress less comfortable for sleeping. Yet another is mechanical contact between adjacent portions of the collapsible springs which, when the mattress is repeatedly compressed, can be noisy and undesirable for a sleeping occupant. Also related to this noise issue is the tendency of the ends of the collapsible springs to suddenly snap off helical interconnecting coils that interconnect the collapsible springs transversely along the mattress. The sudden snapping of these spring ends is not only quite noisy, but also disconcerting to the occupant who may fear that the mattress is about to imminently collapse. An additional shortcoming is the complex, labor-intensive, clip-type connection between longitudinal grid wires and a border wire on each grid.